1. Field of the Invention
This invention relates generally to electrodes for gas depolarized batteries and, more specifically, to a process for manufacturing air electrodes and apparatus for handling the sticky air electrode material during the forming steps of the process.
2. Description of the Prior Art
Typically, the prior art procedures and techniques for making gas diffusion or air electrodes teach applying a paste or slurry electrode mixture, which includes a catalyst and a hydrophobic binder, such as polytetrafluoroethylene, to a large screen, drying the mixture on the screen and then curing or sintering the mixture. The electrode material is then cut into the final electrode sizes. While this process works well for the manufacture of air electrodes, it has certain drawbacks. For example, it is difficult and awkward to dry and sinter the electrode mixture when it is on a large screen. Also the sintering or curing of the electrode mixture must be done in an inert atmosphere in order to avoid oxidization of catalyst in the mixture. This is also awkward and difficult to do because of the large sizes of the uncut electrode. Thus, the difficulties of the prior art techniques of forming an electrode and then sintering or curing are avoided with the present process as it allows one to cure the electrode mixture in the bulk form prior to the forming process.
Also one of the problems with the prior art process is the difficulty in forming a continuous electrode strip.
Another drawback to the prior art process is that when the paste or slurry is heated on the collector screen, there is a tendency of the electrode mixture to contract thus producing cracks in the electrode.
One of the difficulties with heat treatment of the bulk electrode mixture prior to forming the electrode is that the bulk electrode mixture with the hydrophobic binder is very sticky and difficult to handle. That is, the binder material tends to lump or conglomerate thus making it difficult to handle when in a mixed state. Therefore, part of the present invention resides in the fact that I have discovered how to handle and uniformly control the dispersion of the sticky, bulk electrode mixture.
While the present invention relates to use of a fluidized bed for handling the electrode material, it should not be confused with prior art apparatus such as shown in Bahler et al. U.S. Pat. No. 3,551,210. Bahler et al. uses a fluidized bed to aerate or reduce the bulk density of his PVC particles and a comb and vacuum skimmer to produce an even mound of particles. In contrast, the present invention utilizes a fluidized bed to distribute the particle to a uniform depth over a predetermined area so that the particles can be compressed into a self adhering electrode.
Further aspects of the invention include the process itself as well as the apparatus for dispersing and forming the electrode.